Method for the purification of hydrous aluminum chloride

ABSTRACT

In a method for the purification of hydrous aluminum chloride to remove iron, copper and other undesirable trace metals, and any organic contaminants present, hydrous aluminum chloride is precipitated from its aqueous solution by passing hydrogen chloride or a gas containing hydrogen chloride into the solution. The precipitate of hydrous aluminum chloride, which is separated from the aqueous solution by filtration is then washed, and either dried to produce pure aluminum chloride hexahydrate crystals, or redissolved to produce aqueous solutions of purified hydrous aluminum chloride of any desired strength. The iron, copper, and other undesirable trace metals and organic contaminants remain in the mother liquor.

United States Patent Voight et al. [4 Mar. 28, 1972 [54] METHOD FOR THEPURIFICATION OF 1,845,224 2/1932 Blanc ..23/3o0 HYDROUS ALUMINUMCHLORIDE 3,406,010 10/1968 Holderred ..23/143 [72] Inventors: Richard W.Voight, Franklin, N.J.; David OTHER PUBLICATIONS S. H it be B thl h P 0en e e em a Mellor, Comp. Treatlse on lnorg. and Theo. Chem., 1924, [73]Assignee: Pearsall Corporation, Phillipsburg, NJ. Vol. V pages 314 to318. [22] Filed: June 1970 Primary Examiner-Norman Yudkoff [21]Appl.No.: 56,059 AssistantExaminer-S. J. Emery Attorney-Howson & HowsonRelated U.S. Application Data [63] Continuation of Ser. No. 717,021,Mar. 28, 1968, 1 ABSTRACT abandoned In a method for the purification ofhydrous aluminum chloride to remove iron, copper and other undesirabletrace metals, [52] U.S.Cl ..23/300,23/305,23/92 and any organiccontaminants present, hydrous aluminum [51] Int. Cl. 1 "2201f7/62,B01d9/)02 chloride is precipitated from its aqueous solution bypassing [58] Field of Search ..23/9 143, 300, 29255 33152, hydrogenchloride or a gas containing hydrogen chloride into the solution. Theprecipitate of hydrous aluminum chloride, i which is separated from theaqueous solution by filtration is [56] References Cited then washed, andeither dried to produce pure aluminum UNITED STATES PATENTS chloridehexahydrate crystals, or redissolved to produce aqueous solutions ofpunfied hydrous aluminum chloride of any 248,949 7/1881 Newlands desiredStrength. The iron, copper, and other undesirable 558,726 4/ 1896 tracemetals and organic contaminants remain in the mother 1,430,449 9/1922Howard. li 1,403,061 1/1922 Sieurin... 1,697,543 Seidler 1 Claim, NoDrawings METHOD FOR THE PURIFICATION OF HYDROUS ALUMINUM CHLORIDE Thisapplication is a continuation of US. application, Ser. No. 717,021,filed Mar. 28,1968, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to a process for thepurification of hydrous aluminum chloride. More particularly, theinvention relates to a process for the substantially complete removal oforganic contaminants and iron, copper and other undesirable trace metalsfrom spent hydrous aluminum chloride.

By spent hydrous aluminum chloride we mean aluminum chloride hexahydratecrystal or aqueous solution recovered from industrial operations such asthe etching of roofing granules, or bleaching operations such as woolscouring, or generated from anhydrous aluminum chloride on quenching ordrowning organic reactions in which this material has been used as acatalyst.

Hydrous aluminum chloride in both crystal and solution form has longbeen a valuable article of commerce, useful in such diverse applicationsas the manufacture of pharmaceuticals and roofing granules, and inpapermaking and wool scouring for example.

More specifically, hydrous aluminum chloride is available commerciallyas 32 B. solution and as aluminum chloride hexahydrate crystals. The 32B. solution contains about 27.5 percent aluminum chloride and the pureproduct is a colorless crystal clear liquid. Such a solution may beproduced by dissolving anhydrous aluminum chloride crystals in water.The highest purity material previously commercially available, however,is prepared by reacting hydrochloric acid with highpurity hydratedalumina. A typical specification for such material is about 27.5 percentaluminum chloride and about 3 parts per million (p.p.m.) of iron. Thismaterial is available in polyethylene-lined drums, glass carboys, and inrubber-lined tank trucks. Production of the hydrous aluminum chloridesolution has increased markedly in recent years to point where it nowranks with anhydrous aluminum chloride in total tonnage. This solutionis widely used in the soap industry to salt out glycerin lyes, in thepreparation of personal deodorants and antiseptics, as a woodpreservative, in photographic fixing baths and in the manufacture of drycolors, aluminum hydroxide gel, roofing granules and pectin.

Aluminum chloride hexahydrate (AlCl '6H O) which has a formula weight of241.43, contains about 55.23 percent aluminum chloride, and isyellowish-white to colorless, deliquescent, granular crystal or powdermaterial with an odor of hydrochloric acid. The uses of the crystals aresimilar to those of the aqueous solution described above, the solutionbeing generally preferred for ease of handling. The crystals areavailable in polyethylene drums. A typical specification for thismaterial is about 97.2 percent aluminum chloride hexahydrate, about 30p.p.m. iron, and about 0.01 percent insoluble material. The foregoinginformation as to the characteristics of the hydrous aluminum chloridesolution and crystals of commerce is derived from the Kirk-OthmerEncyclopedia of Chemical Technology, 2nd edition, volume 2, page 24,John Wiley and Sons, Inc., New York, N.Y., 1963.

In many of the commercial uses of hydrous aluminum chloride the purityof the material is of the utmost importance. Virgin hydrous aluminumchloride normally contains as the most undesirable impurity about 0.0001to 0.001 percent of iron, and almost equally undesirable, like amountsof copper. The impurities in spent hydrous aluminum chloride are, ofcourse, determined by its history and the application in which it wasused. However, the vast majority of spent aluminum chloride contains asimpurities increased amounts of iron, copper and other metals andorganic impurities.

THE PRIOR ART Numerous proposals have been made for removal of iron fromeither virgin or spent hydrous aluminum chloride. These proposalsinclude treatment of hydrous aluminum chloride solution with theferrocyanides, cyanides and sulfides of potassium and calcium; ammoniumhydroxide and the hydroxides of aluminum, calcium, and manganese; theoxides of manganese, lead, tin and arsenic, and dust forms of aluminum,zinc and iron. All of these procedures are designed to percipitate ironsalts, such as the ferricyanides, cyanides, sulfides and hydroxides.Such precipitates are generally extremely difficult to filter and thesemethods are only effective in uneconomically dilute solutions. Moreover,inasmuch as aluminum compounds coprecipitate with the iron compounds inthese methods, the aluminum recovery efficiency drops sharply when it isattempted to increase the purity of the product. Moreover, suchprocedures are effective only for partial removal of iron and areuseless for the removal of other common impurities. Indeed, most ofthese methods actually contribute additional impurities to the hydrousaluminum chloride solution treated.

The use of both solid and liquid phase ion exchange materials has beendescribed in the literature for the removal of iron from aluminumchloride solution. These methods are also inefficient due to theaffinity of aluminum, as well as iron, for the ion exchange materials.For this reason large quantities of aluminum are removed along with theminor amounts of iron in the solution, thus requiring frequentregeneration of the ion exchange material and, generally, uneconomicoperation. Yet another proposal for the removal of iron from solutionsof aluminum salts has been to add either a liquid ion exchange materialor a chelating agent to the solution and then extract the complexed ironions by means of an organic solvent. This proposal has the samedisadvantages as the other procedures; namely the relative lack ofselectivity of the reagents for iron over aluminum. This method also hasthe disadvantage of contaminating the aluminum salt solution withorganic materials.

The removal of organic impurities from those aqueous solutions ofhydrous aluminum chloride which contain them has also frustrated thoseskilled in the art prior to the present invention. Two principle methodshave been employed heretofore. One involves a stripping or spargingoperation in which steam or an inert gas is passed through the solution.A similar result may be achieved by boiling the solution for a specifiedlength of time and then reconstituting the solution by the addition ofwater. The effectiveness of this procedure is limited, however, sinceonly relatively insoluble or relatively low boiling organic impuritiesare removed. For example, such a method would be ineffectual in freeinghydrous aluminum chloride solution of ethylene glycol or ethylenechlorohydrin, if the solution contained these impurities, as some do.Activated charcoal treatment is also capable of removing as much as -90percent of certain organic impurities which occur in spent hydrousaluminum chloride, but is ineffective for the removal of other commoncontaminants such as glycols.

In all prior processes removal of ionic impurities has been treatedseparately from removal of organic impurities and all generalpurification procedures have been two step processes.

A primary object of the present invention is to provide a process forthe purification of hydrous aluminum chloride by the removal of bothionic (inorganic) and organic impurities, if any, in a simple andeconomical manner. Another object of the invention is to provide aprocess for the purification of spent hydrous aluminum chloride which iscapable of removing virtually all deleterious organic and inorganicimpurities simultaneously.

BRIEF SUMMARY OF THE INVENTION We have discovered that the above andother objects of the invention can be accomplished by precipitatinghydrous aluminum chloride from its aqueous solution by passing a streamof hydrogen chloride gas into the solution, recovering and washing theprecipitate, and thereafter, either drying the purified crystals ordissolving them in water to provide aluminum chloride solutions of anydesired concentration. Whereas virtually all of the prior art procedureshave attempted to remove impurities, essentially one at a time, fromsolutions of hydrous aluminum chloride, our radically different processis based upon the surprising discovery that it is possible to remove thealuminum chloride from the solution and leave the impurities behind inthe mother liquor.

The purification process of the present invention can be practicedeither batchwise or continuously and, as indicated above, is essentiallyindependent of the source of the aluminum chloride or its prior history.Moreover the new process can be employed to purify aluminum chloridevirtually without regard to the concentration of aluminum chloride inthe solution treated.

The purification of hydrous aluminum chloride, according to the processof the present invention, by precipitation from its impure aqueoussolutions is effectively accomplished by using either wet or dryhydrogen chloride gas, or even dilute gas mixtures containing hydrogenchloride and inert gases such as nitrogen and air, for example. Aparticularly attractive and economicalsourcc of hydrogen chloride gasfor use in the process of the present invention is a byproduct streamobtained during the substitutive chlorination of hydrocarbon materials.

The following specific examples of the process of the present inventionare illustrative only, and are not to be construed aslimiting the scopeof the invention.

EXAMPLE I A sample of commercial technical" grade 27.5 percent (32 B.)hydrous aluminum chloride was analyzed and found to contain 0.0004percent iron (as ferric ion). Dry hydrogen chloride from a cylinder ofthe compressed gas was sparged into 1,000 grams of the aluminum chloridesolution at the rate of 300 grams per hour. The solution became quitewarm as a pure white precipitate began to form. After about 1.5 hoursthe rate of hydrogen chloride absorption became very low as indicated bythe fact that the solution had returned to room temperature and theincrease in weight of the solution had leveled out. The percipitatedaluminum chloride hexahydrate was collected on a funnel and washed withseveral small portions of 36 percent hydrochloric acid. After drying ina vacuum oven overnight, the yield of dry product was 495 grams (99.3percent of theory). Analysis of this product for iron failed to indicateany detectable iron in the product. The analytical technique, which isknown to those skilled in the art as the thiocyanate method, is believedto be capable of detecting the presence of iron at concentrationsconsiderably less than 0.00001 percent, and is described in StandardMethods of Chemical Analysis, N. H. Furman, editor, vol. 1, 6th edition,page 552, Van Nostrand Co., 1963. The mother liquor weighed 775 gramsand contained 35 percent hydrochloric acid. Analysis for iron showed themother liquor to contain about 0.0005 percent, essentially all of theiron which had been initially present in the commercial hydrous aluminumchloride solution. The solution also was found to contain only about0.35 percent AlCl EXAMPLE 11 A sample of spent aluminum chloridesolution, obtained from a process in which anhydrous aluminum chloridehad been used in the manufacture of anthraquinone dyes, was analyzed.The solution was bright yellow in color, contained about 30.0 percentAlCl and was contaminated with about 0.0330 percent of iron and about0.004 percent of copper. Hydrogen chloride gas was sparged through a1,000 gram sample of this material in a manner similar to that describedin Example 1. After 1 hour during which 300 grams of hydrogen chloridegas had been added, the reaction mixture was allowed to cool to roomtemperature. The precipitated aluminum chloride hexahydrate wascollected on a funnel and washed with several small portions of 36percent hydrochloric acid. The resulting pure white product was dried ina vacuum oven at 60 C.

The yield was 525 grams (98.9 percent of theory) of a free flowingmaterial that assayed 102 percent aluminum chloride hexahydrate. Neitheriron nor copper was detectable in the product. The test for copper wasmade by conventional procedures on an atomic absorptionspectrophotometer. Further, the impurity (presumably organic) which wasresponsible for the bright yellow color of the original solution hadalso been removed. As in Example 1, virtually all of the iron and copperoriginally present in the spent aluminum chloride solution was accountedfor in the acidic mother liquor.

EXAMPLE III A sample of spent aluminum chloride solution, obtained froma process in which anhydrous aluminum chloride had been employed tocondense benzene with ethylene oxide, was analyzed. This solution wasbright yellow in color and contained about 0.0420 percent iron, about0.0018 percent copper and about 29.6 percent AlCl The solution had anabsorbance of 3.95 arbitrary units at 240 mu in the ultraviolet and 2.31arbitrary units at 420 mu in the visible range. As in the previousexample, 1,000 grams of this solution was treated with 300 grams ofhydrogen chloride gas during a period of 1 hour. The precipitate wassimilarly collected on a funnel and washed with concentratedhydrochloric acid. In this case, however, instead of drying thecrystals, they were transferred to a flask and dissolved in sufficientdeionized water to make 1,000 grams of solution. Analysis of theresulting clear colorless solution showed it to contain about 29.3percent (99 percent of theory) AlCl Tests for iron and copper werenegative. Absorbance in the ultraviolet region showed the peak at 240 muto be 0.19 arbitrary units indicating a 95.4 percent removal of theimpurity responsible for that peak. The absorbance at 420 mu was 0.048units indicating about 97.6 percent removal of the impurity responsiblefor that peak.

EXAMPLE IV A sample of spent aluminum chloride solution obtained from aprocess in which anhydrous aluminum chloride had been used in thesynthesis of dodecylbenzene was obtained. This solution was a dullyellow-brown in color and contained about 30.0 percent AlCl about 0.0175percent iron and about 0.0072 percent copper. Spectroscopic analysisshowed the presence of a compound absorbing at 240 mu to the extent of 11.3 arbitrary units and another at 420 mu to the extent of 2.45arbitrary units. Precipitating the aluminum chloride hexahydratecontained in 1,000 grams of this solution, and proceeding as in Exampleii] there was obtained a 99.1 percent recovery of the aluminum chloride,essentially free of iron and copper, and from which 91.3 percent of thematerial absorbing at 240 mu and 100 percent of the material absorbingat 420 mu had been removed. I

EXAMPLE V A sample of spent aluminum chloride solution was obtained froma process in which anhydrous aluminum chloride had been used in thepolymerization of terpenes to low molecular weight hydrocarbon resins.This was a rather dilute solution containing only about 6.4 percent AlClabout 0.0030 percent iron and about 0.0008 percent copper. Spectroscopicexamination showed materials absorbing at 240 mu, 222 mu and 320 mu withabsorbences of 2.39, 7.34 and 0.051 arbitrary units respectively. Into a1,000 grams of this solution was passed 500 grams of hydrogen chloridegas during a period of 100 minutes. The resulting pure white precipitatewas collected on a funnel, washed with 36 percent hydrochloric acid anddried to yield grams (94.5 percent of theory) of aluminum chloridehexahydrate essentially free of iron and copper. The crystals weredissolved in water to make a 27.5 percent solution and the spectroscopicanalysis rerun. The impurity absorbing at 240 mu had been removed to theextent of 97 percent, the impurity absorbing at 222 mu had been 90percent removed, and the impurity absorbing at 320 mu had beencompletely removed.

EXAMPLE VI This example illustrates the use of byproduct hydrogenchloride in the purification of hydrous aluminum chloride. A 4-literresin flask was charged with 1,500 grams of a C-15 normal paraffin andabout 0.1 percent benzoyl peroxide was added. While heating to 65 C.,with agitation, chlorine gas was sparged into the reaction mixture atthe rate of 250 grams per hour. After an induction period of 50 minutesthe reaction became self sustaining and byproduct hydrogen chloride wasemitted at about 125 grams/hr. The exit line from the chlorinationreactor was connected to a sparger immersed in 100 grams of commercialtechnical aluminum chloride solution containing about 0.0004 percentiron. Aluminum chloride hexahydrate soon began to precipitate. After 1hour, the precipitate was collected on a funnel and dried in the vacuumoven at 60 C. overnight. As in Example I, a 99 percent yield of aluminumchloride hexahydrate was obtained and the product was essentially freeof iron.

EXAMPLE Vll This example describes the fairly large scale semicontinuouspurification of spent aluminum chloride. The aluminum chloride solutionwas derived from a commercial process in which anhydrous aluminumchloride had been used as catalyst to condense ethylene and benzene toform ethylbenzene. The solution was pale yellow in color and containedabout 24.7 percent AlCl,,, about 000530 percent iron and about 0.0037percent copper. The solution also had a very strong benzene odor. Apilot plant for the chlorination of waxes and parafi'rns in whichhydrogen chloride is a byproduct was started up. Ordinarily when inoperation this pilot plant delivers the byproduct HCl to an absorptiontower where it is dissolved in water and emerges as 36 percenthydrochloric acid. When the pilot plant was producing 30 pounds per hourof HCl gas steadily, the water in the absorption tower was replaced bythe spent aluminum chloride solution, which was pumped into the tower atthe rate of lbs. per hour. The resulting aluminum chloride hexahydrateprecipitate was washed downwardly in the tower by the liquid phase andcollected in a rubber-lined centrifuge. After an hours operation, thetower was switched back onto water and concentrated hydrochloric acidwas produced for 15 minutes. This acid was used to wash the cake andthen the tower was switched back to spent aluminum chloride solutionwhile the centrifuge was emptied. The moist cake was dissolved in waterand a small amount of alumina hydrate was added to adjust the pH to 0.8.

During 3 cycles a 98.7 percent recovery of the available aluminumchloride as a 27.5 percent solution was realized. The purified solutionwas clear and colorless, contained no detectable amounts of iron orcopper and was free of undesirable odors.

The foregoing illustrates the practice of this invention which, however,is not to be limited thereby but is to be construed as broadly aspermissible in view of the prior art and limited solely by the appendedclaims.

What is claimed is:

1. A process for separating aluminum chloride from organic contaminantsand at least one other contaminant selected from the group consisting ofiron, copper and other metals having soluble chlorides, which comprisesintroducing hydrogen chloride gas into an aqueous solution containingabout 6 to 30 percent by weight of aluminum chloride containing saidcontaminants to percipitate crystalline hydrous aluminum chloride,separating the precipitated hydrous aluminum chloride, washing saidhydrous aluminum chloride with hydrochloric acid, and drying the washedcrystals to obtain in substantially quantitative yield, substantiallypure hyldrous aluminum chloride free of said contaminants, w ereby theresidual iron content 15 reducible to less than 0.00001 percent.

